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_Physiology Exam 5 > 4/16: Regulation of Extracellular Fluid Volume and Osmolarity > Flashcards

4/16: Regulation of Extracellular Fluid Volume and Osmolarity Flashcards

1
Q

What happens if ECF volume is high?

A

urine excretion rate will increase to compensate

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2
Q

What happens if ECF osmolarity is low?

A

sodium excretion rate will decrease to compensate

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3
Q

Describe this

A

Dotted lines: consumption of isotonic saline solution
- Urine flow rate: increase in urine flow because of volume increase. Helps eliminate volume without changing osmolarity
- Plasma osmolarity: does not change (isotonic)
Solid lines: consumption of water
- Urine flow rate: increase because kidneys secrete dilute urine to get rid of excess urine
- Plasma osmolarity: drops and removes signals for ADH

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4
Q

What is ADH secretion varied based on?

A

Omsolarity and plasma volume
!!Is more sensitive to change in osmolarity than change in volume!!

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5
Q

What does a change in osmolarity cause?

A
  • Increase ADH secretion when osmolarity increases (via increased water excretion)
  • Decrease ADH secretion when osmolarity decreases
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6
Q

What does a change in plasma volume cause?

A

Increase in ADH secretion when plasma volume decreases (via decreasing water excretion, so increasing plasma volume)
Decrease in ADH secretion when plasma volume increases

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7
Q

What is ADH secreted by?

A

neurons that have cell bodies in supraoptic and paraventricular nuclei

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8
Q

What are drops in volume and high osmolarity detected by?

A

baroreceptors and osmoreceptors and will stimulate ADH secretion

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9
Q

What are factors that increase ADH secretion?

A
  • **Increase in ECF osmolarity
  • **Decrease in blood volume (via drop in ANP)
  • Decrease in blood pressure (via drop in baroreceptor activity)
  • Angiotensin II (stimulates aldosterone production which stimulates Na reabsorption)
  • Nausea, hypoxia, nicotine, morphine
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10
Q

What are factors that decrease ADH secretion?

A
  • Decreased ECF osmolarity
  • Increased blood volume (via increase in ANP)
  • Increased blood pressure (via increase in baroreceptor activity)
  • Ethanol, cold temperatures
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11
Q

What is syndrome of inappropriate ADH (SIADH)?

A

syndrome where there is too much ADH secreted from the hypothalamus, causing over-reabsorption of water and excreting concentrated urine

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12
Q

What is SIADH seen in?

A

neurologic disease, head injury, lung tumors (secrete substances that act like ADH receptor agonists) or after major surgery

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13
Q

What does excessive secretion of ADH cause?

A

hyponatremia, decreased plasma osmolarity and urine hyperosmolarity

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14
Q

What is treatment for SIADH?

A

ADH inhibitory drugs (demeclocyline)

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15
Q

What is the defect in SIADH?

A

o Sodium handling is intact and the only defect is in water excretion
o Feedback inhibition of ADH does not occur, so ADH secretion will still occur

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16
Q

What is diabetes insipidus?

A

syndrome where there is not enough ADH secreted from the hypothalamus, causing dilute urine excretion

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17
Q

What are symptoms of diabetes inspidus?

A

Polyuria (urinating a lot), nocturia (awake frequently at night), polydipsia (drinking a lot)

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18
Q

What are types of diabetes insipidus?

A
  1. Hypothalamic/central
  2. Nephrogenic
  3. Polydipsic
19
Q

What is hypothalamic/central DI?

A

defect in ADH synthesis/release

20
Q

What does hypothalamic or central DI a defect in?

A

ADH synthesis or release

21
Q

What does hypothalamic or central DI result in?

A

Depressed plasma ADH levels

22
Q

What is hypothalamus or central DI a problem in?

A

Hypothalamus

23
Q

What is nephrogenic DI a defect in?

A

defect in ADH action

24
Q

What is nephrogenic DI a failure of?

A

maintain hyperosmotic medullary gradient because collecting duct cells cannot recognize ADH

25
Q

What does nephrogenic DI result in?

A

Elevated plasma ADH levels

26
Q

What is nephrogenic DI a problem in?

A

Kidney

27
Q

What is polydipsic DI?

A

compulsive water drinking (behavioral). Maintaining a hypoosmotic ECF causing ADH levels to be low and high urine excretion rate

28
Q

What is polyuria?

A

excretion of more than 3 L of urine/day

29
Q

What is urine volume determined by?

A
  • Amount of solute that has to be excreted (obligatory volume)
  • Concentration of ADH in the plasma (if ADH levels remain high throughout the day volume of urine will be low, if ADH levels remain low throughout the day volume of urine will be high)
30
Q

What are the 3 major mechanisms of polyuria?

A
  • Decrease in sodium reabsorption, which would therefore increase salt and water excretion (kidney diseases, diuretics)
  • Reduced ADH secretion
  • ADH resistance (Through medications: Lithium and tetracyclines. Also seen with Hypercalcemic nephrogenic DI)
31
Q

What is the compensatory mechanism to regulate Na concentration?

A

**1. Osmoreceptor-ADH system
**2. Thirst mechanism
3. Aldosterone and AngII
- Alter Na+ mass accompanied by volume changes (thirst, ADH)
4. Salt appetite

32
Q

What is thirst?

A

Conscious desire for water that restores ECF volume losses

33
Q

What does a drop in plasma volume activate?

A

AngII via baroreceptors

34
Q

What does an increase in plasma osmolarity activate?

A

Osmoreceptors and ADH

35
Q

What does entering of water intake by GI tract cause?

A

More water intake the less thirsty one is

36
Q

What initiates drinking behavior?

A

Hypothalamic thirst center response to signals

37
Q

What is thirst increased by?

A

ECF hyperosmolarity, decreased EC volume, decreased MAP

38
Q

How does Ang II increase thirst?

A

Acts centrally

39
Q

What are stimuli that increase salt appetite associated with?

A
  • Sodium deficits (ECF osmolarity lower than normal)
  • Decreased blood volume
  • Decreased blood pressure associated with circulatory insufficiency
40
Q

Describe what occurs with an increase in osmolarity and no change in volume

A
41
Q

Describe what occurs with a decrease in MAP and no change in volume or osmolarity

A
42
Q

Describe what occurs with an increase in blood volume and no change in osmolarity

A
43
Q

Describe what occurs with an decrease in volume and an increase in osmolarity

A
44
Q

Which changes in systemic control factors would occur in an individual suffering from dehydration

A

Decreased ANP levels
Increased renin secretion by JG cells
Increase SNS activity
ADH levels will be high

_Physiology Exam 5 (10 decks)

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